Conventionally, a battery system for cooling a battery cell is disclosed in JP-A-2003-346759 and JP-A-2003-71674. The system includes an assembled battery having multiple battery cells, which are electrically coupled with each other, and a blower for blowing air to the assembled battery. When the assembled battery generates heat caused by large current, each battery cell is cooled by the blower. Each cell includes a positive terminal and a negative terminal, which protrude from the surface of the cell. The positive terminal of one cell is electrically coupled with the negative terminal of adjacent cell with a bus bar so that the cells are coupled in series with each other. Thus, an electric power density of the assembled battery is large, and the assembled battery supplies high voltage to a motor of an electric vehicle or a hybrid vehicle. The air blowing from the blower passes through a ventilation passage so that the air flows on an outer surface of the assembled battery. Thus, the bus bar protruding from the outer surface is exposed to the air so that the heat is discharged from the bus bar. Thus, the battery cell is cooled.
In the battery system, when the bus bars exposed on the surface electrically short, insulation in the assembled battery is broken. Thus, the performance of the battery is damaged.
For example, when the blower blows air to the battery under a condition that dust, dirt and/or dewdrop are generated, electric insulation between the bus bars and/or terminals may not be sufficiently secured. Further, it is required for the assembled battery to generate high electric power, and also it is required to minimize the dimensions of the battery so as to have high mounting performance. In view of these requirements, the distance between the bus bars and/or terminals is reduced. In this case, it is difficult to secure the electric insulation in the assembled battery.